In an inkjet printer, in order to achieve consistent ejection of ink from the printhead, precise control of the static pressure of ink is required at the ejection location. In a printhead such as described in EP 1224079 and EP 1366901 precise control of the ink flow is also required. Experience has shown that the pressures at the printhead described in EP 1224079 and EP 1366901 need to be correct to about ±20 Pa and those periodic variations must be below about ±2 Pa to eliminate visible variations in print quality.
A simple method of controlling the pressure of the ink supplied to a printhead is to use gravity. An ink reservoir, whereby the surface of the ink is open to atmospheric pressure, is mounted either above or below the level of the printhead in order to generate a positive or negative ink pressure, as required by the printhead. The required inlet pressure at the ejection location can be set by mechanically adjusting the relative height of the ink reservoir with respect to the printhead. The reservoir may also be supplied with ink by a pump.
Some inkjet printers require ink to flow continuously through the printhead and this requires the printhead to have both an inlet and an outlet to allow ink to flow in and out of the printhead. In these printers the pressure of the ink at this outlet can also be controlled by gravity by allowing ink to flow to atmospheric pressure from the outlet tube to a defined level below the printhead. This level can also be mechanically adjusted to achieve the correct operating conditions (such as ink pressure and flow rate) at the ejection location.
Known disadvantages of a gravity-fed system are:                Changing the pressures requires physical movement of the reservoirs.        The location of the reservoirs is determined by the required pressures.        A large volume of space may be required to accommodate the total adjustable range of the reservoirs.        Priming printheads with ink can be assisted by supplying ink at pressures that are very different from the pressures required during printing. With a gravity-fed system a large amount of space and typically a significant amount of time is required to move the reservoirs to achieve these pressures.        The surface of the ink must be open to the atmosphere, increasing the risk of dust or other contaminants polluting the ink.        
WO 97/44194 and EP 1092548 describe ink supply systems in which the ink is maintained at a constant level or height in the reservoir by use of a weir; however, these systems all use gravity to set the pressure at the ejection location.
WO 2006/030235 describes a system where the pressure of the ink at the inlet and outlet of a nozzle containing fluid supply apparatus is controlled by controlling the pressure of the air above a weir at the inlet and the outlet from the nozzle containing fluid supply apparatus. In order to maintain the functioning of the weir it is necessary to remove the ink that has flowed over the weir from the reservoir.
WO 2006/030235 describes how this can be done by allowing the ink to be sucked back to the main ink tank through a flow restriction by lowering the pressure of the ink in the main ink tank. However, the rate at which ink is drawn from the reservoirs into the main ink tank will depend on the position of the ink tank relative to the reservoirs, which will require the amount of restriction to be compensated to account for this. In addition, the rate at which ink is drawn from the reservoirs into the main ink tank will depend on whether gas or ink is passing through the flow restriction at any particular moment. This fluctuation in flow rate will tend to lead to fluctuations in the pressure in the reservoir unless the pressure is controlled very carefully with a control system with a very short response time.
In order to avoid this problem a method using floats is presented in WO 2006/030235. The height of these floats is monitored using sensors, thus avoiding the over flow from being drained insufficiently quickly or air being withdrawn. However including floats and sensors increases the cost of the system and can introduce additional failure mechanisms.
WO 2008/035120 discloses an ink management system for supplying or receiving liquid at a controlled pressure comprising a closed reservoir, a weir disposed in the reservoir and configured to separate the reservoir into a first and a second chamber, the first chamber having an inlet for receiving liquid from a first remote location, and the weir being disposed such that the level of liquid in the first chamber can be maintained at a constant height, wherein the reservoir is sealed from the surrounding atmosphere and the system further comprises a pumped outlet disposed in the second chamber and arranged to remove liquid and gas contained within the reservoir.
The advantage of having a reservoir with a weir that is independent of the surrounding atmosphere is that the pressure of the ink can be controlled by adjusting the pressure of the gas over the surface of the ink without having to adjust the height of the reservoir or weir. Controlling the pressure of the gas may involve a pressure sensor, an actuator and some control electronics arranged in an active feedback loop to control the pressure.
The ink pressure control apparatus close to the printhead (often called a Local Ink Feed, or LIF) has to control ink pressure accurately and reliably for the printhead to function correctly.
Typically, known LIFs are assembled from discrete components supported on a metal chassis, interconnected with flexible tubing to carry ink, rinse fluid and air between the components. To facilitate connection, components are typically fitted with barbed tube connectors or mounted on manifold blocks as appropriate, adding to the component count. The large number of components and connectors, together with the constraints on their relative positions from fluid flow considerations, results in a complex assembly that is expensive to manufacture, difficult to assemble and service. It is also heavy and large, forcing the local ink feed to be located separately from the printhead whose pressure it regulates, resulting in inaccurate pressure control at the printhead caused by pressure drops in the connecting tubes. The large size of the LIF also causes the printer equipment to be undesirably large. A further problem is that fluid connectors are prone to trap air bubbles leading to unreliable ink flow to the printhead.
The present invention aims to overcome one or more of the problems identified above, namely to produce a pressure control apparatus with increased reliability, to create an apparatus that is compact, lightweight, and which can, preferably, be integrated with the printhead itself, and to produce an apparatus which is much lower cost and is very simple to assemble.
According to the present invention, there is provided an apparatus for controlling ink pressure in a printhead, the apparatus comprising an integrally formed structure having at least one control reservoir separated into first and second chambers by a weir, at least one inlet passageway, extending from the first chamber to an inlet port on an edge of the structure, for supplying ink from a remote source into the first chamber of the reservoir, at least one fluid outlet passageway, extending from the second chamber to an outlet port on an edge of the structure, for recirculating fluid from the reservoir to the remote source of ink; and at least one ink connection passageway, extending from the first chamber to an ink supply port, for supplying ink to, or receiving ink from, a printhead.
According to a further embodiment of the present invention, there is provided an apparatus for controlling ink pressure in a printhead, the apparatus comprising an integrally formed structure having at least one control reservoir separated into first and second chambers by a weir, at least one inlet passageway, extending from the first chamber to an inlet port on an edge of the structure, for supplying ink from a remote source into the first chamber of the reservoir, at least one fluid outlet passageway, extending from the second chamber to an outlet port on an edge of the structure, for recirculating fluid from the reservoir to the remote source of ink; and at least one ink supply port, in communication with the first chamber, for supplying ink to, or receiving ink from, a printhead.
Thus the present invention overcomes the reliability issues by integrating the LIF into a single component, thereby eliminating internal flexible tubing and connectors and reducing the lengths of interconnections making it considerably more reliable. The elements of the LIF can be arranged in much closer proximity with each other because there is no requirement for access to interconnections for assembly and servicing, so the resultant LIF is much smaller allowing much closer proximity with the printhead itself.
The apparatus preferably comprises at least one ink connection passageway, extending from the first chamber to the at least one ink supply port.
The structure is preferably formed by an additive manufacturing process, such as stereolithography. By manufacturing the structure by an additive process such as, stereolithography, this enables re-entrant features and blind passageways to be created simply and inexpensively inside a single component, typically made of made of lightweight resin.
Each reservoir may have a dedicated inlet passageway and/or a dedicated fluid outlet passageway.
A pressure control system may be provided having a further passageway, extending from the reservoir to a pressure port on the edge of the structure, for sensing the air pressure within the reservoir.
The pressure sensing passageway preferably includes an air chamber. The air chamber preferably includes one or more baffles. The baffles may be angled such that, in use, fluid between the baffles and the pressure port drains back into the reservoir. The use of the air chamber and/or the use of the baffles preferably directly above the control reservoirs stop fluid ingress into the pressure sensor during LIF cleaning operations. A pressure sensor may be connected to or retained within the pressure port.
The apparatus may further comprise a pressure control passage extending from a part of the pressure sensing passageway to a pressure control port on the edge of the structure. The pressure control passageway preferably extends from the air chamber to the pressure control port. Co-location of the pressure sensing elements and pressure control elements, typically at the top of the apparatus, again means that the component count can be reduced, as no pressure isolation valves are required. This further reduces the complexity of the apparatus and reduces the component count.
The pressure sensing elements are typically designed to work with air pressure and it is important to prevent ink and/or rinse fluid from coming into contact with the sensing elements. Previous methods have employed an isolation valve that is closed during automated cleaning operations that introduce rinse under pressure into the control reservoir. However, the co-location of the pressure sensing elements and pressure control elements means that during cleaning operations, the rinse is prevented from reaching the sensor by closing the orifice valve (pressure control element), thereby causing air in the air chamber to pressurise and prevent rinse from entering the air chamber, keeping the sensor dry. This eliminates the need for an isolation valve to be placed between the chamber and the sensor.
Each reservoir preferably has its own dedicated pressure control system.
The apparatus may further comprise one or more passageways for allowing rinse fluid and/or air to flow through the structure for supply to a printhead. Preferably at least one rinse passageway and at least one air passageway are provided. At least one of the rinse and one of the air passageways may merge to form a combined flow. One or more of the rinse passageways may exit into an air passageway. There may be one rinse passageway per air passageway or more than one rinse passage may exit into any given air passageway.
An inkjet printer may be provided including an apparatus according to the invention wherein one reservoir supplies liquid to a printhead and the other reservoir receives liquid from the printhead, thereby controlling the pressure of the liquid supplied to the printhead and the pressure of the liquid removed from the printhead, such that the ink flows through the printhead at a controlled rate and at a controlled pressure.
Alternatively, the plurality or reservoirs may supply different inks to a printhead or plurality of printheads, which may further be supplied with one ink or a plurality of inks, for example, cyan, magenta, yellow and black inks.
The integrally formed structure may be a single structure containing two or more reservoirs, each reservoir having at least one inlet passageway, extending from the first chamber to an inlet port on an edge of the structure, for supplying ink from a remote source into the first chamber of the reservoir, at least one fluid outlet passageway, extending from the second chamber to an outlet port on an edge of the structure, for recirculating fluid from the reservoir to the remote source of ink, and at least one ink connection passageway, extending from the first chamber to an ink supply port, for supplying ink to, or receiving ink from, a printhead.
The integrally formed structure may be a single structure containing two or more reservoirs, each reservoir having at least one inlet passageway, extending from the first chamber to an inlet port on an edge of the structure, for supplying ink from a remote source into the first chamber of the reservoir, at least one fluid outlet passageway, extending from the second chamber to an outlet port on an edge of the structure, for recirculating fluid from the reservoir to the remote source of ink, and at least one ink supply port, in communication with the first chamber, for supplying ink to, or receiving ink from, a printhead.
Each reservoir may have at least one ink connection passageway extending from the first chamber to the at least one ink supply port.
The apparatus may include one or more additional integrally formed structures, each having at least one control reservoir separated into first and second chambers by a weir, at least one inlet passageway, extending from the first chamber to an inlet port on an edge of the structure, for supplying ink from a remote source into the first chamber of the reservoir, at least one fluid outlet passageway, extending from the second chamber to an outlet port on an edge of the structure, for recirculating fluid from the reservoir to the remote source of ink; and at least one ink connection passageway, extending from the first chamber to an ink supply port, for supplying ink to, or receiving ink from, a printhead.
The apparatus may include one or more additional integrally formed structures, each having at least one control reservoir separated into first and second chambers by a weir, at least one inlet passageway, extending from the first chamber to an inlet port on an edge of the structure, for supplying ink from a remote source into the first chamber of the reservoir, at least one fluid outlet passageway, extending from the second chamber to an outlet port on an edge of the structure, for recirculating fluid from the reservoir to the remote source of ink; and at least one ink supply port, in communication with the first chamber, for supplying ink to, or receiving ink from, a printhead.
Each additional integrally formed structure may further have at least one ink connection passageway extending from the first chamber to the at least one ink supply port.
One or more of the additional integrally formed structures may contain two or more reservoirs, each reservoir having at least one inlet passageway, extending from the first chamber to an inlet port on an edge of the structure, for supplying ink from a remote source into the first chamber of the reservoir, at least one fluid outlet passageway, extending from the second chamber to an outlet port on an edge of the structure, for recirculating fluid from the reservoir to the remote source of ink, and at least one ink connection passageway, extending from the first chamber to an ink supply port, for supplying ink to, or receiving ink from, a printhead.
One or more of the additional integrally formed structures may contain two or more reservoirs, each reservoir having at least one inlet passageway, extending from the first chamber to an inlet port on an edge of the structure, for supplying ink from a remote source into the first chamber of the reservoir, at least one fluid outlet passageway, extending from the second chamber to an outlet port on an edge of the structure, for recirculating fluid from the reservoir to the remote source of ink, and at least one ink supply port, in communication with the first chamber, for supplying ink to, or receiving ink from, a printhead.
Each reservoir may further have at least one ink connection passageway extending from the first chamber to the at least one ink supply port.